Auto Sequencing to skip Negatives

[AnhVP]

I've attached a sample of my worksheet. I'm trying to write an auto number for column E "Receipts" to skip rows where receipts are not available, in which case want to display "No Receipt." Let's say Row 6 (Computer Repair) does not have a receipt. Instead of auto generating the auto number for that record as "03", can the auto number skip that record and continue to the next record and generate the next record as "03"?

Is it possible for Excel auto numbering to skip negatives? If so, a true/false column would be needed but how to write the IF or OR function would be a total guess for me.

If I'm already using IF(ISBLANK,"" , would I be able to add another function to display "No Receipt"? I've tried different variants of functions and in the end it's just logical to think that anything I put after IF(ISBLANK,"" would contradict each other.

I think my best bet is to reconfigure the whole sheet. Any help would be greatly appreciated. Thank you.