SoftBank Group Corp. said Tuesday it had failed to declare about ¥40 billion ($377 million) in taxable income in the business year through March 2019.

Tax authorities have found that SoftBank Group overstated foreign exchange losses and made errors in booking costs related to an overseas subsidiary. No additional taxes were levied as the underreported income was offset by losses in the fiscal year, according to sources familiar with the matter.

Of the ¥40 billion, about ¥17 billion was underreported after the group miscalculated the yen value of a dollar-denominated debt it owed to a subsidiary in Japan by applying an incorrect foreign exchange rate, the sources said.

The authorities also did not accept SoftBank Group's booking of about ¥14 billion as expenses for reward payments to an overseas subsidiary that manages the SoftBank Vision Fund, a venture capital fund focused on the technology sector, the sources said.

SoftBank Group said in a statement that it made corrections after the Tokyo Regional Taxation Bureau pointed out the errors, also including in the timing of reporting expenses.

Separately, the group's major mobile phone carrier SoftBank Corp. underreported about ¥3 billion in income, resulting in a back tax of over ¥1 billion, according to the sources. The company said it had filed a correction with the authorities.

The revelations came after SoftBank Group failed to declare about ¥400 billion in taxable income in the business year through March 2018.