At present once we go into a new tax period older invoice lock and are no longer editable. This is reasonable for things like invoice date and line items however it makes little sense to have options such as reminder/thank you emails and online payment options being locked too.
At present if an invoice is locked we can't adjust it to turn on/off Stripe payments or turn on/off email notifications which seem to have nothing to do with any financial information which should be locked and can in fact make it more difficult to receive payments.
I'd therefore suggest those options (for email and online payments) should be moved out of that initial invoice detail or at least be made accessible elsewhere so they can be adjusted once an invoice is in a locked state.
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Thanks for your post and I'm very sorry for the delay in our response.
I do agree that this should be an editable option when an invoice has been sent and locked due to VAT. I will happily flag this with our Development Team.
If you do need the email options turned off, please do drop us an email to firstname.lastname@example.org and we can get our technical team to do this for you.
Any further questions, please do get back in touch.