Special G/L indicator A is reserved for down payments

What causes this issue?

The special G/L transaction types correspond with the special G/L
indicator. The following types have a specific,hard-programmed meaning:

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

A Down payment
W Bill of exchange
Thus, there can be several special G/L indicators for the type 'down
payment but cannot be a special G/L indicator A for the type 'other'.

System Response

How to fix this error?

If the special G/L indicator should belong to the type 'down payment',
assign it to this type.
If the special G/L indicator does not belong to the type 'down
payment',do not use the indicator A.

Error message extract from SAP system. Copyright SAP SE.