Doctor accepts only cash payment, is this allowed?

Hello, so recently I needed to get a form filled by my family doctor and was told I must pay in cash. I wasn't expecting and wasn't carrying any. However I went to my car and dug out all the change I had and luckily I had the $55 required. Then the front receptionist refused because I was paying in too many coins. She made me wait another 15 minutes for the doctor to come and eventually accept the payment.

Now when I went there the next time they had a sign posted no debit/ no e-transer payment accepted.

Are they allowed to do this?