Firebase hosting servers essentially run this command to check the TXT records for your domain:
dig -t txt +noall +answer tennispredictions.eu
If I run this command right now, I get no results. If Firebase servers see the same in their DNS query, they will not be able to continue.
You can also use mcheoolbox to query DNS: http://mxtoolbox.com/SuperTool.aspx?action=a%3atennispredictions.eu&run=toolpage . It also does not give me any results at the moment.
This means that either you have not yet saved / applied your changes, or have not yet propagated everywhere. The longer it takes for the changes, the more likely it is that you still need to take some action from your DNS provider (names.co.uk in your case).
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