Hi freem,
thank you for watching my video and your advices.

I am focusing on the credit / coin routine now and found out the following:

This outputs the credit counter of Player 1
fixPrintf(5, 5, 0, 0,"Credit P1: %06d", volMEMWORD(0xD00034));

This should output the credit counter of Player 2 but it causes a system crash and restart in my code ???
fixPrintf(5, 6, 0, 0,"Credit P2: %06d", volMEMWORD(0xD00035));

The throw-in of one coin increases the credit counter by 256 (decimal) / 0x100 (hex).
The maximum is 39168 (decimal) / 0x9900 (hex) which equals to 99 coins.

After 1800 frames (=30 seconds) the credit counter gets deleted by the System BIOS (?) and contains only 0x0000.
Is this a normal behavior that the credit counter stores the values only temporary?

Do you use the following system commands for your routine?

BIOS_CREDIT_DEC1 ( $10FDB0) (https://wiki.neogeodev.org/index.php?title=BIOS_RAM_locations#BIOS_CREDIT_DEC1)
CREDIT CHECK ($C00450) (https://wiki.neogeodev.org/index.php?title=CREDIT_CHECK)
CREDIT DOWN ($C00456) (https://wiki.neogeodev.org/index.php?title=CREDIT_DOWN)

..