Sparsentan in Posttransplant Immunoglobulin A Nephropathy or Focal Segmental Glomerulosclerosis

Inclusion Criteria: * Willing and capable of giving signed informed consent which includes compliance with the requirements and restrictions listed in the ICF and in the protocol. * Male and female aged ≥18 years * Participants with a kidney transplant with biopsy-proven IgAN or FSGS histological pattern in the graft. * A period of ≥12 months since kidney transplantation. * UPCR ≥0.5 g/g and eGFR (CKD-EPI creatinine-based formula ≥30 mL/min/1.73 m2. * Participants who can become pregnant, must agree to the use of 1 highly reliable method of contraception from 7 days prior to the first dose of study intervention until 30 days after the last dose of study intervention. * Systolic BP ≤160 mmHg and ≥100 mmHg, and diastolic BP ≤100 mmHg and ≥60 mmHg at screening. * For participants on an ACEI and/or ARB, and/or sodium glucose cotransporter-2 (SGLT2) inhibitor, the dosing regimen(s) is stable for ≥6 weeks prior to screening. Exclusion Criteria: * Participant has multiorgan transplants (with the exception of pancreas and corneal transplants). * Immunosuppressive therapy (IST) regimen for kidney transplant or other systemic chronic ISTs including enteric budesonide that is not stable for \>6 weeks prior to Day 1. Exceptions include routine changes in the dose of CNIs to meet target level. * \<3 months after antirejection treatment and active rejection. * Active bacterial, fungal or viral infection and/or active treatment of infection including BK virus (BKV), cytomegalovirus (CMV), human immunodeficiency virus (HIV), Hepatitis B and C \<3 months prior to and during the screening period. * Current treatment for surgical complications. * History of heart failure (New York Heart Association \[NYHA\] Class II-IV). * Jaundice, hepatitis, or known hepatobiliary disease. * Malignancy within the past 2 years with the exception of adequately treated basal cell carcinoma or non-metastatic squamous cell carcinoma of the skin, with no evidence or recurrence. * History of alcohol or illicit drug use disorder (as defined in the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition). * History of serious side effects or allergic response to any angiotensin II antagonist or ERA. * Participant requires any of the prohibited concomitant medications. * Treatment with sparsentan \<12 weeks prior to screening. * Participant has participated in a study of another investigational product \<28 days prior to screening or plans to participate in such a study during the course of this study. * Hematocrit \<27%, hemoglobin \<90 g/L (9 g/dL), or potassium \>5.5 mmol/L (5.5 mEq/L). * The participant is pregnant, plans to become pregnant during the course of the study, or is breastfeeding. * The participant, in the opinion of the Investigator, is unable to adhere to the requirements of the study, including the ability to swallow the study IMP whole. * The participant, in the opinion of the Investigator, has a medical condition or abnormal clinically significant laboratory screening value not listed above that may interfere with the evaluation of sparsentan safety or activity.