In the livestock tracker settings page under Account Mapping Type you have the option to select either Single sales & purchase accounts per stock class OR Individual sales & purchase accounts per stock class.
What each of these options mean
Individual sales & purchase accounts per stock class
Each stock class that you enable in the tracker settings will need to have it's own unique set of sales and purchase accounts e.g. Purchases - Beef MA Cows

Single sales & purchase accounts per stock class
You will have one sales account set up in Xero for the sale of all your livestock, regardless of the stock class e.g. Purchases - Beef

Troubleshooting
I can't find the right account in the drop down box to map an account
Have you set up an account for this in Xero yet? - If you haven't set up an account to map you will need to do this first, then once that account exists in Xero you can run a sync in Figured to pull it through
I have an account in Xero but I still can't see it in the dropdown box
Have you run a sync in Figured to pull it through? - run a sync in Figured
I've run a sync but I still can't see it in the dropdown box
Head to the account configuration page by heading to Settings > Chart of Accounts and check that the account has the correct Account Type set up - Sales accounts will need to be set as Sale account, and purchase accounts will need to be set as Direct cost account
I still can't find the account in the dropdown box
Reach out to the team using the Green Chat bubble and we will see what's going on.