Hi

I'm very new to dnd and still learning the mechanics. I've talked to my DM about my character's weapon, and I'm currently making a sickle of thorn at has a second attack that can use Thorn Whip cantrip as a spell.. but I can't seem to be able to add it on. Is this something that cant be added, or am I doing something wrong?

Thanks for the help in advance

Sammi

Thorn Whip is not a free access* spell. To use it in a homebrew on DDB, you must purchase either the “Full Version” of the PHB from this website, or at least that one spell from the PHB. You can purchase that book by following this link (to see your “a la carte” purchasing options):
https://www.dndbeyond.com/marketplace/sourcebooks/players-handbook

*(The “Basic Rules & SRD” are free access, as are the options from the Elemental Evil Player’s Companion. The PHB is not free access. A large portion of the PHB is also included in the Basic Rules & SRD, but not everything. The full list of available free access spells can be found here:
https://www.dndbeyond.com/spells?filter-class=0&filter-search=&filter-verbal=&filter-somatic=&filter-material=&filter-concentration=&filter-ritual=&filter-sub-class=&filter-source=1&filter-source=4)

Thank you so much for this information 

As usual, happy to help.