Śrīla Ṭhākura Mahāśaya says, śrī-rūpādi mañjarī-gaṇera anugā haiyā, prema-sebā niba cāiyā. “Having longed for it, I shall receive the loving service of Śrī Śrī Rādhā-Mādhava from the mañjarīs led by Śrī Rūpa Mañjarī.” There is a specific reason he has used the words prema-sevā here instead of just sevā.
Prema, love, is the best thing to offer during one’s service to Śrī Bhagavān. If prema does not exist in the sevaka’s heart, then the fruits, water, cooked foods and other articles she offers cannot bring happiness to Śrī Bhagavān.

Therefore, the following has been mentioned in the Padyāvalī:

nānopacāra-kṛta-pūjanam ārta-bandhoḥ
premṇaiva bhakta-hṛdayaṁ sukha-vidrutaṁ syāt |
yāvat kṣud asti jaṭhare jaraṭhā pipāsā
tāvat sukhāya bhavato nanu bhakṣya-peye ||

“O devotee! When Śrī Kṛṣṇa, the friend of the afflicted, is lovingly worshiped with various kinds of articles, his heart melts with joy.
As long as there is strong hunger and thirst in the stomach, food and drink are no doubt enjoyable and satisfying.” (1)

The devotee’s anxious love causes a powerful longing to awaken in Śrī Bhagavān’s heart to accept the articles of worship offered by the devotee.

Śrī Rādhā’s kiṅkarīs are the direct embodiments of sevā-rasa. Their forms are molded from sevā-rasa. The love in their hearts is so pure and exalted that it has reached maturity in the form of sevā. Like iron that has become one with fire, their love and sevā are so similar in nature that they appear as one undivided thing. Therefore, Śrīla Ṭhākura Mahāśaya has used the term prema-sevā. This prema-sevā must be obtained from the nitya-siddhā-kiṅkarīs. The prema-sevā of Śrī Rādhā-Mādhava is the personal treasure of the mañjarīs. It is possible for the kiṅkarī-bhāva-sādhaka to attain this if it is compassionately bestowed by the mañjarīs. By the words prema-sebā niba cāiyā, it has been implied that everything from the sādhaka’s expertise in bhajana to his resultant eagerness for prema is meant to invoke their compassion. Such sādhakas who are eager for kiṅkarī-bhāva must with a sorrowful prayer beg for Śrī Rādhā-Mādhava’s prema-sevā from the mañjarīs. The mañjarīs are also boundlessly merciful; when they see the distress of the worthy new dāsī, they will bless her with the appropriate sevā.
This is the implied meaning of the words prema-sebā niba cāiyā.

(1) Another interpretation of this verse: “When Śrī Kṛṣṇa, the friend of the afflicted, is lovingly worshiped with various kinds of articles, the devotee’s heart melts with joy.” (Translator)

From Prema Bhakti Candrikā by Śrīla Narottama das Ṭhākura Mahāśaya with the Sudhā kaṇikā vyākhyā tika by Srila Ananta das Babaji

Translated by Haricarana das