All that stuff at the beginning looks like you are thoughtful about some details. This is of no help at all
I keep on getting error msg.
Provide the error number and/or description (never just the error number). If you show code about an error make sure you identify the line that causes the error. Now to your question:
Is Customer_ID text data type or is it number data type? If text, try
DoCmd.OpenReport "rpt_invoice", acViewPreview, , "[Customer_ID] = '" & [Customer_ID] & "'"
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.