Non-PRO English to Spanish Art/Literary History Ancient Egypt

Hi! I'm translating a text regarding the history of beer and I came across the following sentences:

"Egyptian workers were paid with clay chits that they reimbursed for beer. Chits were worth 5 gallons."

I found "chit" is "a signed voucher of a small debt (as for food)" (Merriam-Webster), usually translated as "vale" or "pagaré", but since these were made of clay, I find it confusing.
I first thought it could be some kind of coin and translate it as "ficha", but according to what I've read, egyptians didn't have coins at that time (3000 BC).
Is it possible these were clay tablets with writing on it that they used as paychecks? Does it sound too bad if I translate it as "pagarés de arcilla" or "cheques de arcilla"?

I hope there's somebody who knows more about History than me that can help me. I'm open to all kinds of suggestions.

Thank you in advance!