Unable to charge the speaker
Make sure that the AC adaptor is connected securely to the speaker. Then, make sure that the AC adaptor is connected securely to an AC outlet.
The speaker supports USB AC adaptors that are capable of delivering an output current of 3.0 A or 1.5 A. (Using a USB AC adaptor capable of delivering an output current of 3.0 A for battery charging reduces the charging time.) Be sure to use a USB Type-C® cable (compliant with the USB standard) that supports the output current of your USB AC adaptor. Use of a USB AC adaptor with an output current of less than 1.5 A is not guaranteed for battery charging. The charging time may vary depending on the ambient temperature or the usage of the speaker as well.
Depending on the type or specifications of a commercially available USB AC adaptor, if you use the speaker at a loud volume, the remaining power of the rechargeable built-in battery may decrease or the speaker may turn off even while the speaker is connected to an AC outlet by the USB AC adaptor. This, however, does not indicate a malfunction. If such a case occurs, turn off the speaker and let the battery fully charge itself before you use the speaker.