I don’t know how to undo Automatic credit allocation to sales invoices since it comes automatically on invoices i make to one client hence affecting my accounts receivables. Kindly explain to me what it means and how i can do away with it.
You have basically two options, allocate the payment from customer to Customer credits account and in this case Manager will allocate the amount automatically among outstanding invoices. Or allocate the payment from customer to Accounts receivable account which will allow you to match payment against specific invoice.
If you want more granular control over how payment is allocated, you need to use Accounts receivable account.
Also, you can mix & match. For example if client paid $1,500 and $500 is for one specific invoice and $1,000 can be matched automatically, then allocate $500 to Accounts receivable against specific invoice and $1,000 to Customer credits against customer.
Have a look at Guides | Manager