Unable to pair individual AirPods together at the same time.

Hello. I have a left AirPods and right AirPod from different sets. Both are gen 2. I can pair each, individually, with my iPhone, but I cannot pair them together. This means only one plays at a time. I have tried resetting them according to Apple's instructions, and when I put both into the case (which is fully charged and plugged-in), the light blinks amber. Holding down the button on the case for as much as 15 or 30 seconds doesn't change the light.

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