It appears to be a system error that needs to be fixed.
I registered another one of my clients and partners with OneBox OS:
https://dropdoterra.1box.link/desktop/He received a letter, but when he tried to follow the link in the letter, he gave a 404 error.
client provided screenshot
The client performed these dances with a tambourine and only they helped
***
1. Go to the OneBox website
https://crm-onebox.com/ and log in to your personal account
2. Return to the mailbox and repeat the link in it
3. After that it will probably work
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but these are very complex actions and some users at this stage may refuse to use the program
pliz simplify the algorithm so that you do not have to do so many linear actions