This is a clinical research study for an investigational drug called RAP-219 in adult participants with focal seizures. This study is being conducted to determine if RAP-219 is safe and effective in reducing focal seizure frequency.

Approximately 312 subjects will be randomized into one of two active treatment groups or placebo in a 1:1:1 randomization ratio (Medium Dosage, Low Dosage and Placebo). After completing the Double-blind Treatment Period, participants will either transition into the RAP-219-FOS-901 long-term safety (open-label extension) study or enter the 8-week post-treatment Follow-up Period of this study.

Inclusion Criteria:

1. Age 18 - 75
2. BMI 18-45 kg/m2
3. Diagnosis of focal epilepsy for ≥24 months prior to Visit 1
4. Report from at least 1 brain MRI or CT scan and 1 EEG study, each completed within 10 years prior to Visit 1, consistent with focal epilepsy diagnosis
5. Concomitant use of between 1 and 3, inclusive, antiseizure medication(s) ASM(s) as maintenance, not including rescue or pro re nata (PRN) ASMs
6. Ability to keep accurate daily focal seizure records using an e-diary

Exclusion Criteria:

1. Known hypersensitivity or prior exposure to RAP-219.

2. Unstable or uncontrolled serious medical, neurologic (other than focal epilepsy), or psychiatric condition that is ongoing or considered likely to recur

3. Anticipated need for surgery during the study period

4. Medical history of any of the following:

   1. generalized epilepsy
   2. focal preserved consciousness without observable manifestations (also known as focal aware nonmotor) as the participant's only seizure type
   3. psychogenic nonepileptic seizure (PNES)
   4. status epilepticus or seizure clusters (when individual seizures cannot be counted) within 12 months prior to Visit 1 (Day -56).
   5. epilepsy surgery within 12 months prior to Visit 1 (Day -56).

5. Participation in another clinical study of an investigational product within 12 weeks or 5 half-lives of this other investigational product