All Newsletters stopped sending, are paused

I have been sending newsletters for several months but just realized, that the automated newsletters and the subscription emails have stopped sending a few weeks ago. So like 70 new subscribers never had the chance to finish their subscription, and those about 75 who had already subscribed, didn’t get their newsletters.
I tried to send a newsletter manually but same there. The status is on “paused” although the newsletters are set on “active”. I checked my mailpoet account but couldn’t find any problem there. The settings seem to be right, too. I am absolutely clueless about what causes the problem. Can anybody help, please?

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