Wifi provisioning failed message on Galaxy 8

My husband and I both have Galaxy 8's with ATT service. We've had the phones a year. Originally, wifi calling helped with our inconsistent phone mobile service at home, but now I'm unable to turn on wifi calling on either phone. Wifi is stable and speed test is acceptable. HD voice is on. Whenever I try to turn on wifi calling, I get a message of 'wifi provisioning failed. Try again later.'

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