There’s 2 reasons for this.
1) cable degradation. If you pinch a wire too much it’ll break and there will be no connection. So try to not bend your wires at too hard an angle.
2) lint gets in the charging slot. It can often seem as if the cable you’re using doesn’t work but what’s actually going in is impacted lint is keeping the cable from contacting the right spots. To fix that, take a bobby pin and gently scrape out the lint until you’ve removed it all.
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