Short answer:

• Sampradya (sampradāya) means a “tradition” or spiritual lineage in Jainism.
• Gaccha (Gachcha/gaṅa) is a specific monastic lineage or sub-group within a Jain sect (in Digambara it is commonly used; in Śvetāmbara it is also used for major sub-orders).

What this means in Digambar Jainism:

• Gaccha/gaṇa: A living line of mendicants and their lay followers tracing back to a particular teacher or founding monk. It prescribes certain ritual calendars, practices, and customs, but does not usually change core Jain doctrine.
• Examples of Digambara gacchas/gaṇas (historical lineages): Mula Sangha (which itself split into sublineages such as Nandi, Sena, Simha, Deva Sangha), Kashtha Sangha (including later branches), and Dravida Sangha. There are other smaller lineages like Balatkara Gana and Deshiya Gana, each with its own historical spread and centers.
• Function: Gacchas organize monastic life, pilgrimage routes, temple practices and festival schedules, while the essential Jain vows and metaphysical principles remain the same.

What sampradaya means here:

• In Digambara practice, the term sampradāya is less common than gaccha for naming sub-groups, but it still denotes a “tradition” or teaching lineage within the Digambara world (which Acharyas, texts, and commentaries are emphasized in that tradition).
• In Śvetāmbara Jainism, sampradāya is often used to describe larger sectarian families and their doctrinal/ritual orientations; Digambara Jains focus on gaccha/gaṇa as the main structuring terms.

Key idea to hold:

• Sampradaya = broad tradition/teaching lineage.
• Gaccha = specific monastic lineage within a tradition, with distinctive practices and calendars but not different core doctrines.

If you want, I can point to a JainKnowledge page that explains gaccha and sampradaya in more detail.