Hi john.ellis
I hope you are well mate.
Here is a video I recorded a while ago on No series setup: https://www.youtube.com/watch?v=71DlbLYjLKA&t=4s
Generally speaking you should consider searching Manual Setup

In here check all the No Series settings for example under Purchase & Payables, or Sales & Receivables and ensure a default No Series is set.
If the No Series is selected > and the No Series selected is setup properly, you shouldn't have any prompts requiring a user to manually make up numbers.
I hope this has answered you questions
Thanks JC
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