Bitcoin deposit stuck 0 confirmations high confidence/low priority
Miners naturally select the  highest fee transactions to include in the blocks they create.  At 300 sat/byte, the fee you paid is too low for the transaction to be immediately included in a block.  

See https://core.jochen-hoenicke.de/queue/#8h to visualize the current set of transactions waiting to clear.  As you can see, transactions at your fee level have not been reliably clearing since ~7h ago.