Decades ago I worked for a small company and this would drive us all to distraction.
It's standard policy for big companies to delay payment. Our usual delay was 3 months after invoice even though our terms were strictly 30 days from the end of the month.
We had a process in place to mitigate this.
The first was to offer an early payment discount if invoice was settled in full within 30 days.
Then we had a robust system of reminders. The first reminder went out promptly the day after the 30 days.
The second went out two weeks later and was in red ink.
The third was two weeks later and was a notice of us taking action via the small claims court for unpaid invoices and asking them to contact us urgently.
Then the last was us taking them to court.
Invoices were almost always settled before the last letter. Most would pay with the early discount incentive.
Chasing unpaid invoices took a lot of my time!
You have to have robust retrieval systems in place as if they went into receivership you'd never see the money owed. The quicker it's settled the better.