I will supply you that information, but be warned without buying a new print head first is a total waste of time, money and most importantly ink..
PM on the way..
The Pro 1 is not a Pro 10, and won’t tolerate any interference, it needs a new print head and they are no longer available.. Refurnish print heads from all other sources are Caveat Emptor..
An alternative answer would be to print a self-adhesive label in black with white lettering reversed out and stick the label onto the black envelope.. Quickest option..
P.S. envelopes won’t wear your laser printer out..
I ordered a couple of rolls of filament from a company in the UK, I had been using them quite a bit before Brexit, but this time it took 3 weeks for the delivery to arrive at twice the normal charge rate, seems it went to Germany by road fright first and then to Dublin by DHL Air fright.. Brexit...
Try closing the tray and holding the Resume button in for 3 seconds, if that doesn’t work then power off the printer for 5 minutes and then power on and see if the error message has gone..
Try running that scan test print again on ten plain paper sheets, then run another nozzle check and see if there’s a big difference..
Al printers use a lot of ink when you try to unclog them, the answer is don’t let them clog in the first place, run a test print weekly..
On 1… All I can say is go to https://www.octoink.co.uk/..
That’s a one stop shop for all your ink and sundries supplies.. O’ Plus good advice..
On 2… maybe @palombian will help out there.. I don’t have a good track record with the Pro 10..