When laying an accumulator sequentially, when one leg of the accumulator loses we stop laying our bets.

When laying our bets sequentially the games must not overlap and you would lay them one leg at a time, in order of play, when the results of the previous leg in your accumulator are known.

Firstly, to clear up some jargon, a Leg refers to your selected game, so in the example image below the First Leg of your Accumulator (Acca) would be the FCB Magpies v Dundalk game, and your selection would be Dundalk being the Away (A) team.

Next regarding the above image again, the ACCA TYPE is all you should need to change depending on the type of offer or bet you are doing, you're probably familiar with the type of bets from the regular calculator, i.e. Normal/Qualifier, Risk-Free, or SNR (Stake not returned Free Bet)

Lay Sequential is the equivalent of Normal/Qualifier - using it you would expect a small qualifying loss, and would usually use it when qualifying for Free Bet or refund
Lock In, this is sort of the equivalent of Risk-Free Mode, you should only ever use this on an Insurance offer (where you're getting a refund if exactly 1 leg loses)
Lay Sequential Free Bet is the equivalent of Stake Not Returned (SNR) and should only be used if you are using a Free Bet.

Step by Step Laying of the above Example

No matter which mode you have selected, the Acca Finder will update the calculated lay stakes to suit the offer type, the actual process of sequential laying (laying the legs in sequence) is the same.

I'll leave this in lay sequential (qualifier) mode for this example, however, if it were a free bet you were using and you changed the acca mode, you would see the expected return (retention) from the free bet in the EV and QL boxes, they will turn positive and change to green, this would now be showing the expected retention of the free bet instead of a qualifying loss, and the lay stakes themselves would be lower as they are being calculated to underlay, the same as SNR mode does for a single bet.

So in that above example, you have backed the acca at the bookmaker, you then would go to the exchange you've chosen and lay Dundalk with a stake of £17.51 at Odds of 1.92.

Wait for the result of the game, let's assume that Dundalk did win, you then mark the leg "W" as it was your selection that Won, the Acca Finder will then show your next lay stake which you are now due to lay on Cincinnati the Home (H) team you have in the second Leg.

You should then go to the exchange and check the lay odds for Cincinnati in case they need to be updated, let's say they have changed from the original 2.02 and are now 1.98. Go back to the acca calculator you are using and update the lay odds and click to confirm re-calculate if required. Some calculators will auto update, the Acca Finder asks you to confirm - so it now looks like this.

Now you should go to the exchange and lay Cincinnati with a stake of £34.65 at the Odds of 1.98, then again you wait for the result of that game.

Scenario 1. If Cincinnati win the game

Then you would repeat the above steps, mark the second leg as won and you will be shown the next lay stake.

So You are now going to be laying G-Osaka the Home (H) team, pop over to your exchange and check the lay odds and update the calculator if required, then as in the above example, you would be laying G-Osaka at odds of 2.08 with a stake of £69.29. This is the acca finished and no matter the result of the last game there will be a total qualifying loss of £2.16. You will either win the acca bet at the bookmaker and lose all the liabilities on the 3 legs for the £2.16 loss or you will win that last LAY stake £69.29 which will cover the £20 back stake and the first 2 legs liabilities for the £2.16 loss.

Scenario 2. If G-Osaka do not win their game (lose or draw)

Then you will be finished with this bet and would not need to place any further lays. If you mark the leg as lost in the Acca Finder you would see that there would be no next lay stake given and there will be a message to confirm you should STOP LAYING, how much your qualifying loss is, and if there is any reward attached to the type of bet you are doing.

In the image above it tells you to stop laying and that your qualifying loss is the £2.15 you were expecting. This is the win of the second leg lay stake minus the liability of the 1st leg and the £20 back stake at the bookmaker.

Summary

 
No matter the size of the Acca or the type of offer, it's about choosing the correct calculation method then it's just laying the legs in sequence until the acca is complete or one leg has lost.

One thing to be aware of is the total liability required when laying accas, there may be times you do not need to lay all the legs, and so have a lower liability needed, however, you should always make sure you have enough balance in the exchange to cover the whole bet if needed. This is always roughly the same (it's actually a bit less, but as a general rule of thumb) as what the actual back bet would return if it were to win in the bookmaker, so for the above bet £25 x 6.47 = £161.75 should be more than enough to cover the liability, and allow some extra in case of odds changes.

Lastly, once you have started an Acca do not forget to lay a leg as you could end up losing more than your back stake if there are already lost liabilities!

It can seem daunting at first, but it's simply following the same routine.