To manage without an inverter and charge your bike almost directly from solar (soldering and electronics skills needed) I would consider an adjustable DC/DC converter.

1. Small step-down converter with current limit:

Input voltage range: 6-40.00V
Output voltage range: 0V-32.00V
Output current: 0-5.1A
Output power range: 0-160W

www.aliexpress.com/item/1005006294300036.html

2. Big step-down converter with current limit:

Input voltage: DC12-80V (can not be used for 72V battery)
Output voltage: 2.5V-50V adjustable (only buck) (maximum output voltage = input voltage * 0.8)
Output current: 20A (MAX) 25A overcurrent
Maximum power: 600W
Conversion efficiency: ≥ 93%

www.aliexpress.com/item/1005007391865816.html

3. With serious and silent cooling, dual displays (voltage and current), adaptive current limiting that considers temperature, input up to 120 V DC (be careful, this voltage level is deadly):

Input: DC 25-120V
Output: DC 1.2-75V adjustable
Current: 20A (MAX)
Power: 600W (Reduce current based on heat dissipation when voltage difference is high)

www.aliexpress.com/item/1005010659062631.html

The downside of a simple converter is that it doesn’t know about the optimal loading point of your solar panel (doesn’t do MPPT or maximum power point tracking). If you want that (it gives 30% more productivity), consider an entry level solar charge controller, but it must support 48V battery mode (I notice that your charger outputs 63V, the termination voltage of a 48V battery is usually 64V) and manual fine adjustment of the termination voltage (to bring it lower).

This might work since it appears to have a “user” (user defined) battery type:

www.aliexpress.com/item/1005010080097662.html

Manual here to find out if it actually would:

nikom.biz/…/Homysun-MPPT-Solar-Charge-Controller-…

Note: dial in less than your full battery voltage and don’t push the Chinese products to their maximum advertised current. Your upmost output voltage + voltage ripple + measurement error must stay below the full battery voltage. Of course, you must have a balancer and BMS (to stop everything in an emergency) on your battery. I also recommend a timer.

If you need to step the panel voltage upwards, consider a “boost converter” or “step up converter” instead, or wire two panels in series and use a step down converter.