See update from February, 2024 here:

To get an additional 90-day extension (updated May 24, 2023): After your initial 90 days have expired, you may extend your visa by visiting a migration office. You have from day 91 up to 20 days after your initial visa expires, to extend your visa. This is known as the grace period. The cost is about US $150. There are a few migration offices in the area. The nearest one to Fruit Haven is in Zamora, and there are others in Cuenca, Loja, and Quito. The location of the office is subject to change within each city, so you may want to confirm the office’s location at the tourist information office of the city in which you choose to extend your visa.
Visa extension requirements:

• A photocopy of the two data pages of your passport (the ones with your signature, photo, and identification information)
• A photocopy of the entrance stamp in your passport of when you last entered Ecuador
• Around US $150 cash (as of May 2023)
• Proof of payment for the visa extension, which is a small receipt issued by a bank or similar institution (see instructions below)

Visa extension instructions:

1. Gather all your required documents and funds (except the proof of payment, which you will obtain later).
2. Visit your preferred migration office (Servicio de Apoyo Migratorio). This cannot be done at an immigration office. The closest migration office to Fruit Haven is the one in Zamora, which is three hours away by bus. The following instructions will be for the office in Zamora.

In Zamora, the small migration office is inside a large building called Gobernación Zamora Chinchipe, directly next to Parque Central Zamora. Walk up the stairs and into the building, and turn right. Walk all the way down the hall and on the right, you will find a small migration office.

Ask the clerk for the cost of the visa extension (prórroga de visa) just in case the bank charges you a different amount than what the clerk told you. Also, ask the clerk to write down the name and address of the closest bank or other institution that will accept this payment for you (if you do not, it may be difficult to find). Then, ask the clerk to write down their name and phone number just in case the bank needs to call them.

3. Go to a small store called Cyber, on the bottom level and northern corner of a big orange building directly across the park from the migration office. Tell the clerk you are paying for the extension. Make sure the amount they tell you matches the one from the migration office. If not, tell them to call the migration clerk using the phone number you obtained earlier. Pay for the extension and get the receipt. You must have this proof of payment to present to the migration clerk.

4. Bring the proof of payment, along with the other required documents, to the migration office. They will probably remember you from your last visit. They will hand you a simple form to fill out. Once you fill out the form and the clerk processes your documents, they will hand you your proof of extension, a passport-sized slip of paper that reads, “Comprobante de Prórroga.” Congratulations, you can now stay in Ecuador for an additional 90 days.