It's nice to have you here on the Community page, @usernoshbox.lufkin.
The way how invoices were sent to customers affect the availability of the invoice or payment link. Usually, when you enable your account for e-invoicing, the Pay Now button is added to the invoice or reminder sent to the customer. If the link becomes unavailable, the email preference may be set to HTML or Plain Text.
Let's try checking your Account and Settings and see if there are changes made to your Sales Preferences. I'm here to help guide you on how.
Once completed, try sending an invoice reminder from the Invoices tab.
Besides, I would recommend checking that the payment options appear on the invoice and have a check-mark placed in the box next to them.
To know more about the process, feel free to open this article: Take and process payments in QuickBooks Online.
You can as well open this link to learn more about the deposit times for customer payments.
If you need additional help from me, please feel free to add a comment below if you have any other questions. Keep safe!