Mailmerge OR query formatting

[Matt Volatile]

Dear All,

Can anyone help me simulate an OR command in a Mailmerge field, please? I
can't quite seem to get my head around the required syntax.

I currently have the following command:

{ IF {MERGEFIELD Booker_Booking_Method } = "Manual Invoice" "AAHCONF/09/{
MERGEFIELD "unique_ID" }/{ MERGEFIELD "membership_no" }" "N/A" } to produce
invoice numbers on receipts.

I need to an a simulated OR clause that also returns the invoice number if
Booking_method equals "Online Invoice". Where do I nest the command?

Thanks in advance for your help!