Capacity error on My Passport external drive

I use two identical My Passport 0.5 TB disks to back up an older MacBook Pro laptop (OS X Version 10.11.6). One of them I back up using the WD SmartWare, and for this one I do it using the Mac’s Time Machine. However, when I plugged it in yesterday I turned on the WD SmartWare by mistake. No backup has actually happened, but when I attempted to start the Time Machine backup instead I got a message that 0 KB were available. I manually removed two previous backups, leaving only the most recent two, but this has only freed 115 KB: I still get a message that 499.06 GB are used. I then connected the drive to a more recent MacBook Pro (10.13.6) and got the same result. I checked the disk using the First Aid function on the Disk Utility App of the latter laptop and found no problem with the disk. Thank you for your help!

Hi @arieh,

I request you to please share screen shot of error message to assist in better way.

Please refer below link to know WD Smartware End of Support:

Hello!

Hello @Keerti_01,

Thank you for responding to my posted inquiry. I sent back the screen shots you requested back on August 24. Please let me know if you can address my question now or if you need additional information.

Thanks again!

@arieh