There are two main reasons for Monero transactions can take a long time to send. First, Monero transactions are very complex and require a lot of computing resources. This means that older devices will take a considerably longer amount of time to create a transaction than a newer device. Second, Monero transactions are private by default, and that requires both interacting and mixing your transaction with other pending transactions on the Monero network. As a result, both internet connection quality and the sheer number of pending transactions on the Monero network itself can impact how long it takes to complete a transaction.
After attempting a send, please be patient and let it process. Some older devices can take several minutes to complete before showing a success message.